The present invention relates to projectiles and in particular to projectiles having a tubular housing.
It is known to equip a missile with propulsion systems such as a ramjet. This known missile is initially launched by a rocket to a speed sufficient to initiate operation of the ramjet. This known missile is not a tubular device fired from a barrel, but is instead part of a larger warhead delivery system. Simple tubular projectiles are also known. However, such projectiles have inherently limited range due to their aerodynamic characteristics. A known tubular projectile includes a ramjet fueled by internal liquid fuel. However, it requires conduits and pressurized tanks and is therefore relatively heavy and complicated. Recently, solid fuel propellants have been employed in ramjets, but primarily for missiles driven by an integral rocket ramjet.
The present invention provides a simple and aerodynamically stable projectile by employing a tubular housing having an internal layer of combustible material. The projectile is launched through a barrel by means of a structural member that detaches after launch. In the disclosed embodiment the structural member is an obturator-sabot containing a pusher. Once launched, supersonic airflow entering the tubular housing is decelerated, compressed and therefore heated. This event ignites the layer of combustible material causing thrust by means of a ramjet action.
By employing such an arrangement, a gun-launchable projectile is provided which has unique characteristics by virtue of its ramjet-produced thrust. An important application for such a device is as a practice round for simulating the time and spatial flight characteristics of a combat service projectile.
Simulation of APFSDS projectiles (armor piercing fin stabilizied, discarding sabot projectile) is difficult to achieve safely because of its high density, inherently high ballistic coefficient and low velocity decay. A conventional scaling approach to simulation would result in a practice round which is so dense or heavy that the practice round is nearly as lethal as the actual combat service projectile. When use is made of a scarce target, such as an obsolete or worn-out tank, it is important to avoid immediate destruction of such a target by an energetic and lethal practice round. It is also important to limit the range of the practice round because of the limited real estate available for test purposes.
A disclosed embodiment of the present invention avoids the foregoing problems with a light projectile that produces thrust. Instead of using large masses or high densities to simulate a given ballistic coefficient, thrust is produced at a magnitude slightly less than the associated aerodynamic drag, in one embodiment. Thus, the relatively small velocity decay of a heavy projectile is simulated by a significantly lighter projectile. Moreover, the range of projectiles incorporating principles of the present invention can be limited according to the quantity and burn time of the ramjet fuel. Once this fuel is expended, the high aerodynamic drag associated with the tubular housing of the disclosed embodiment causes it to fail. Thus, a relatively light practice round incorporating principles of the present invention can be safely fired at rated muzzle velocity on a relatively small practice range without causing excessive damage to a target. Using such an arrangement, the projectile weight can be reduced by a factor of 1/8 to 1/10 while the effective kinetic energy is reduced by a factor of 1/10 to 1/14.
In a preferred embodiment used as a practice round, the nose of the projectile is made of a frangible honeycomb material to reduce the initial impact upon a target.
Also, in a preferred embodiment, a discarding sabot is employed to allow the firing of a sub-caliber practice round. Employing such a sub-caliber round results in a less massive and consequently less lethal projectile.
Furthermore, other embodiments can be designed as an air defense round. The tubular housing and ramjet fuel can be arranged so that the housing and its internal combustion products pierce and explode within a target. In such an embodiment, the ramjet thrust can be set equal to or, preferably, greater than the aerodynamic drag to reduce the transit time.